# Homework Help: Convection, Conduction, Radiation

1. Dec 30, 2011

### Dberry

In my book I'm reading about heat, specifically convection. There is an image of a person with a drink in their hand, suntanning while a fan blows on them. I get that the drink represents conduction, the sunlight is radiation, but how is the fan convection?

2. Dec 30, 2011

### LawrenceC

When a fluid passes by a solid object of different temperature, heat passes to or from the solid ojbect to the fluid by means of convection. Convection can be either natural or forced. With wind, it is forced. With still fluid but different temperatures, there is a change in the density of the fluid at the solid. That causes natural convection.

3. Dec 30, 2011

### LawrenceC

There is natural convection inside the drink cup due to the difference in temperature between the container wall and neighboring fluid.

Last edited: Dec 30, 2011
4. Dec 30, 2011

### Dberry

I still don't understand. Can someone dumb this down for me?

5. Dec 30, 2011

### Dberry

I have the definition and examples of convection in my book. I guess the air is the build medium but how is the fan blowing on the tanning person convection? Where is the warm air and where is the air moving?

6. Dec 30, 2011

### Dberry

by build I meant FLUID

7. Dec 30, 2011

### cupid.callin

I might be wrong so if i am LawrenceC correct me

Conduction is when particles pass on heat by vibrating at their places
Convection is when instead of vibrating the particles move to exchange heat ... as in case of fan !!!

8. Dec 31, 2011

### LawrenceC

The temperature of the ambient air (fluid) is different from the surface temperature of the human body. Therefore the fluid being pushed over the skin's surface by the fan will exchange heat with the body, either warming it or cooling it. Because there is a fan, the convection is considered forced convection. If the fluid is moving only due to density differences, the convection would be called natural convection.